The invention relates to interchangeable gear driven platens in typewriters and printers which automatically compensate for the varying available platen gear diameters, upon insertion of the platen and platen gear into the typewriter or printer.
The rotation of the platen has been accomplished in the past by either a pawl driven ratchet which is rigidly attached to the platen for driving the platen or by a gear driven platen drive. Pawl driven platens have heretofore had the advantage of interchangeability to be capable of changing the amount of line feed while gear driven platens do not provide for ready changability of the gears to easily facilitate the change of the line feed increment. When a gear driven platen is replaced to change the line feed, the gear drive chain must be adjusted to insure proper engagement of all gears and generally requires trained service personnel.